Is there some reasonably accurate ballparking formula to allow for quick conversions between IAS and TAS as a function of pressure altitude and difference of ground temperature relative to standard atmosphere? That is,
E.g. "for each 1,000ft subtract X%, for each degree F/C subtract Y%" so that if I'm at 8,000ft and ground temperature is 10 C, I simply subtract 8X% and add 5Y% to get a good approximation.
My idea is to have a quick ballpark to start working with, in case there is no time to start fiddling with the flight computer, or in cases where the error would be insignificant for practical purposes.